Reliable body area networks using relays: Restricted tree topology

This paper focuses on mechanisms that support the reliable transfer of data for medical applications in wireless Body Area Networks (BANs), in particular for the monitoring by sensors of vital life signs. Recent studies on path-loss models for BANs show that for some scenarios a Star Topology (ST) with a direct, single link, between sensor and coordinator is insufficient. It is thus beneficial to extend the ST to a Tree Topology with a restricted number of hops using relays. In this paper we provide an overview of relevant findings before presenting our Restricted Tree Topology (RTT) design. We then present an experiment that is set up to study the performance of RTT in terms of availability of connectivity, based on Received signal strength at 2.4 GHz using wearable channel sounders with various people sleeping - sleeping has been found to be one of the most difficult scenarios, in terms of reliability, for BAN. Our simulation results show that for certain sleeping positions, RTT improves connectivity by approximately 12% for a receiver sensitivity of -95 dBm. In addition we have shown that without RTT it is not possible to meet the reliability requirement as set out by the IEEE 802.15.6 Task Group for its draft standard.